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Olenick, Laura

Abstract

Organic-inorganic hybrid molecules are of increasing interest due to the ability to increase the dispersion of the inorganic component in a system which would ordinarily lead to aggregation. A well-dispersed and well-understood system is important in industry for ease of manufacturing as well as for customer satisfaction. In The Structure and Rheology of Complex Fluids, Larson uses the example of toothpaste. Unless the components of the toothpaste are evenly dispersed with even texture, consumers will not purchase the product.
The goal of this research is to synthesize, characterize and study the properties of organic-inorganic hybrid molecules. These novel nanoparticle-organic hybrid molecules, or NOHMS, were synthesized using silica, a triethoxysilane-terminated poly(ethylen glycol), a poly(hexyl methacrylate) polymerized using atom transfer radical polymerization(ATRP) of hexyl methacrylate.
Scheme 1. A Schematic Diagram fo the Prepar c for ration of SiO2-PEG-PHMA Nanoparticle-Organic Hybrid Molecules (NOHM MS).
Six samples are discussed here of varying molecular weights of poly(hexyl methacrylate) (PHMA). These six samples targeted degrees of polymerization of PHMA of 5, 7, 9, 11, 15, and 20. Each sample contained approximately the same amount of poly(ethylene glycol) (PEG). Three samples of poly(ethylene glycol) monomethyl ether-b-poly(hexyl methacrylate) (MPEG-PHMA) are also discussed here for comparison purposes. Thermogravimetric analysis (TGA) shows a percentage of weight remaining after heating to 550 debree C indicating presence of inorganic material in the hybrid samples. TGA of the free samples show 100% weight loss by 400 degree C.
Differential scanning calorimetry (DSC) of the hybrid samples showed one glass transition temperature (Tg), a melting point, and a crystallization point for each sample. The Tg was found not to correspond to the Tg of PEG or of PHMA. The crystallization point was found to depend on volume fraction of the silica. Dynamic light scattering (DLS) measurements show a single, though broad, peak with an average radius of around 30 nm. FT-IR shows peaks in the NOHMS consistent with SiO2-PEG-PHMA. Using rheology, the hybrid molecules were found to have yield stresses that are dependent upon the volume fraction of the silica core. The rheology of the free block copolymers did not show a yield stress for any of the samples.